The bloodshed occurred on Saturday in Beni, a flashpoint city in North Kivu region. The Congolese army has blamed the Allied Democratic Forces (ADF), a notorious rebel militia.
The latest violence, which sparked local anger, comes just three months before the Democratic Republic of Congo holds a fractious election to choose a successor to Joseph Kabila, the country’s deeply-contested president.
It also prompted NGOs in Beni working to fight the spread of Ebola to halt their work following a health ministry request, although Doctors Without Borders (MSF) was operating as normal in treatment centers some 30-50 kilometers (20-30 miles) outside the city.
Witnesses said Saturday’s violence began in the city center in the late afternoon with the attackers using guns and machetes.
An initial army estimate put the toll at 18 dead, including 14 civilians and four soldiers, but later raised it to 21, including 17 civilians.
“The front line is no longer in the Virunga National Park and is now in Beni, which poses a real danger for the holding of safe elections on December 23,” said Anselme Mwaka, an opposition MP from the Union for the Congolese Nation (UNC).
Social networks buzzed with comments denouncing the apparent powerlessness of the army and perceived silence of the authorities.
“Kabila and his cronies dare to suggest that the situation is getting better yet these dramas are taking place every day. How can they live with this responsibility?” tweeted exiled opposition leader Moise Katumbi.
Patrick Nkanga Bekonda, a Kabila adviser, suggested there were local and external forces trying to provoke civil conflict in the troubled city.
“We can see the hallmarks of both local and external involvement in the ‘Somalisation’ of Beni, despite efforts to reduce these killings,” he said.